Re: [v4] mm: khugepaged: avoid overriding min_free_kbytes set by user

[Vijay Balakrishna]

On 9/17/2020 2:28 AM, Michal Hocko wrote:
> On Wed 16-09-20 23:39:39, Vijay Balakrishna wrote:
> > set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
> > user.  Post start-of-day THP enable or memory hotplug operations can
> > lose user specified min_free_kbytes, in particular when it is higher than
> > calculated recommended value.
>
> I was about to recommend a more detailed explanation when I have
> realized that this patch is not really needed after all. Unless I am
> missing something.
>
> init_per_zone_wmark_min ignores the newly calculated min_free_kbytes if
> it is lower than user_min_free_kbytes. So calculated min_free_kbytes >=
> user_min_free_kbytes.
>
> Except for value clamping when the value is reduced and this likely
> needs fixing. But set_recommended_min_free_kbytes should be fine.

IIUC, after start-of-day if a user performs
- THP disable
- modifies min_free_bytes
- THP enable
above sequence currently wouldn't result in calling init_per_zone_wmark_min.

Thanks,
Vijay